The present invention relates to metal vapor discharge devices, and more particularly, to a laser device having an enclosure which confines the liquid metal of the laser device to a location whereby the temperature of the liquid metal may be elevated so that the liquid metal transitions from its liquid state to its vapor state thereby allowing it to advantageously contribute to the production of lasing.
One of the most critical components in metal vapor lasers is the vacuum discharge cell which contains a liquid metal. The vacuum discharge cell should confine the liquid metal to a heated region wherein it is subject to temperatures higher than the melting point of metal so that the liquid is transitioned into its vapor state whereby it is enabled to contribute to the intended lasing. Some liquid metals suitable for the use in metal vapor lasers are chemically reactive and vaporize at relatively high temperatures. At these temperatures, the liquid metal is free to flow wherever it can as determined by gravity, the orientation of the vacuum discharge cell, and the surface tension of the liquid metal. Unless means are provided, the liquid metal may disadvantageously flow out of the heated region of the cell and thereby not contribute to the generation of lasing. To prevent migration of the liquid metal out of the heated region of the cell, usually a small amount, commonly termed a "sample," of liquid metal is used and the entire vacuum discharge cell is held in a horizontally level position. Unfortunately, maintaining the discharge cell in the horizontal level position unduly restricts the orientation that may be desired for the metal vapor laser. Historically, several techniques have been used to impede the flow of liquid metal from the heated region when the vacuum discharge cell is oriented to a position other than horizontal.
A laser device having the capability of maintaining a laser medium, such as a liquid metal, in a desired discharge chamber of the laser device in spite of being moved or tilted is disclosed in U.S. Pat. No. 4,696,011 ('011). The laser device of the '011 Patent utilizes a porous element that absorbs the laser medium in its liquid state so that it is always present in the discharge chamber. This device has a disadvantage that the porous metal element may contaminate the liquid metal. In addition, high surface tension liquid metals sometimes cannot be made to "wet" the porous element and also large samples of these liquid metals must sometimes be used.
Another technique for impeding the flow of liquid metal from the heating region of the vacuum discharge cell, is the use of inner and outer concentrically nested ceramic cylinders, with special hole configurations placed into the inner cylinder. The liquid metal is then confined in a well (created by the hole placed through the inner cylinder) and the wall of the outer cylinder. Sometimes, a ceramic compound is used to seal the gap between the inner and outer cylinder portions located around the well. Disadvantages of this method include possible contamination of the liquid metal by the ceramic sealing compound, leakage of an extremely low surface tension liquid metal into the gap region between cylinders, and, more importantly, limitations on the orientation of the vacuum discharge cell away from the restrictive horizontal level position.
Another technique employs the use of various materials to form a "dee"; that is, a small longitudinally sliced tube having sealed ends. This dee contains the liquid metal and is placed in the heated region of the vacuum discharge cell. Disadvantages of this technique include inhibiting a clear path in the discharge region, sometimes referred to as blocking the clear viewing aperture, and the limitation of the vacuum discharge cell being oriented away from the restrictive horizontal level position due to the sample size, wall height of the dee, and the means by which the dee is secured inside the vacuum discharge cell.
Still further, heat pipe ovens have also been used not only to contain the liquid metal in the heated region, but also to recycle their produced recondensed metal vapor back into the heated region of the cell. These devices consist of a screen-like material, called a wick, which lines the central region of the vacuum discharge cell with a large quantity of liquid metal to "wet" the wick. Capillary action allows recondensed metal to be drawn back into a heated central region of the vacuum discharge cell. One disadvantage of this technique is the difficulty in finding a suitable wick material that will not contaminate the liquid metal being used, and yet still be manufactured with appropriate spacing to allow the capillary action to occur. The wick also causes a potential hazard when used in a discharge plasma. More particularly, the wick presents an alternative low resistance path which disadvantageously allows for a discharge to conduct along this path rather than to be used for breaking down the vapor so that the vapor can contribute to the desired lasing. In addition, careful attention must be given to the thermal gradient through the vacuum discharge cell to ensure that recondensation occurs on the wick material. Since gravity affects the distribution of the liquid metal on a wick, vacuum discharge cell orientation is again restricted to being near horizontal level position.
It is desired that means be provided to allow the liquid metal of the metal vapor laser device to be confined within the heated region of the device without suffering any of the disadvantages of the prior devices. Further, it is desired this means be easily implemented to accommodate different vacuum discharge cells having different dimensions.